Whats the best approach towards modeling this exercise in prepoMax?

General Questions
1

I Have been thinking on using plane stress but i am not sure if this is the right way to do this, what do you think? Am studying Link 1.

I used as boundary condition “fixed“on the top of the handle and surface traction forces at pins location, should I put forces in an angle?

Thank ahead to anyone that answers :smiley:

pictures removed due to OP’s request

Multibody parts connection
2

Regular spanners/wrenches are very common examples of plane stress analyses (assuming they are thin). Even in this thesis: https://kann.dk/files/P7_54b_FINAL.pdf

What is the source of this exercise ?

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3

Thanks for your answer!!, do you have any advice on how to imitate the study they did on the book?

4

You show vertical forces Fh in the drawing that are missing in the model. The sum of the reactions does not add up.

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5

Can you share your file ? I see that you also added a slot they don’t include. You could partition the edges to apply the forces to smaller regions if needed. And play with the vectors to incline them properly.

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6

CrimpingTool
CrimpingTool1783×1096 196 KB
I had a little play around having copied ur geometry and changed it a little. Not sure it is an approach that is any use to any one but I found it quite entertaining

crimpingtool.pmx (4.5 MB)

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7

Mesh from Mecway ? I see that you modeled joints as rigid body constraint with common REF NODEs (Abaqus wouldn’t allow it, but CalculiX doesn’t mind). I just wonder why they are defined using custom keywords. To remove ROT NODEs ? If they are not explicitly defined, CalculiX adds them internally. Their coordinates are irrelevant anyway (because the rotation occurs about ROT NODE).

Mkraska has a nice way of modeling such joints with coupling constraints: CalculiX-Examples/Test/Joints at master · calculix/CalculiX-Examples · GitHub

However, for the OP, it might be better to start from that one piece.

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8

yea -my work flow is to normally to take a 2d part, make a quick quad mesh in rhino then build that into a 3d mesh in mechway. I used custom keywords for the rigid body connectors and removed the ROT NODES as I did not want to limit the rotations and could not think of a faster way to approach it. In mecway there is a fancy API script that makes “spiders” and i often use that but i was all out of ideas in PPmax -i will take a look at the reference u posted-thanks for the ref

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9

Mkraska’s approach is really good to model pinned joints. Pretty much only disadvantage is the amount of work to define all the couplings if there are multiple joints.

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10

I recreated the geometry from fatmac’s file and made some quick setup for you to begin with:

Crimping tool Norton v2.pmx (3.7 MB)

Try playing with different BCs and other settings - I left some deactivated on purpose.

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11

Thank you so much for your answer!!!

12

thank you for taking your time to answer!!!

13

thank you so much, how did you manage to get the dimensions of the geometry? if am not wrong the geometry is not completely described in the book.

Thanks for the help, now i will do my best to figure the rest by myself, this is part of a project we are doing and i really want to learn !!

14

I took it from fatmac’s file. But since there are some dimensions, you can import an image to CAD software, scale it vased on these dimensions and draw over the picture to get a sketch of the whole geometry. I can show you the workflow in FreeCAD if you want.

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15

wow, that’s so smart, please that would really help me, i would really like to learn how to do it by myself!!

Thanks a lot for the help seriously!

16

This is what I did with fatmac’s file (the steps are meant for FreeCAD 1.2.0 dev version because it has some additional helpful tools for sketches):

  1. Export this mesh part from PrePoMax to STL:

export STL
export STL1451×660 121 KB

  1. Import it to FreeCAD as STL Mesh.
  2. Go to the Part workbench and apply the following tools in this sequence:
    a) Shape From Mesh
    b) Convert to Solid
    c) Copy → Refine Shape

As a result, you will get a solid CAD part with some redundant faces:

image
image1211×535 13 KB

  1. Now to extract its bottom face for 2D model, use the Facebinder tool in the Draft workbench:

image
image1274×554 18.4 KB

Part Design → Subshapebinder would also work.

However, there are those redundant edges, so I did this:

  1. Create a sketch on the XY plane.
  2. Use External Projection in the Construction mode to project all the edges of that face (this is only possible in FreeCAD 1.1.0 or newer):

image
image1198×561 6.09 KB

  1. Now the manual part - take the Line tool and draw over the straight segments (between their endpoints). Then take the B-spline tool and draw over the curved segments (here you can skip some endpoints if you don’t mind lower accuracy).

spline
spline971×557 7.24 KB

For the holes, just round their diameter and make some of their projected points coincident with the newly drawn circles.

End result:

image
image899×410 1.37 KB

  1. Now use Part → Face From Wires to get the face that you can export to STEP for use in PrePoMax as a 2D model:

image
image823×406 1.44 KB

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17

And this is how you can do it based on the image:

  1. Import the image to FreeCAD (File → Import).
  2. Double-click on it, select calibrate, pick 2 points whose distance is provided and enter it:

calibrate
calibrate1277×653 101 KB

  1. Create a sketch on the same (XY) plane and now you can draw over the image using the Sketcher tools.
  2. Once you’re done, exit the sketch (make sure it’s closed) and use Part → Face From Wires to get the face as mentioned above.
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